The present application relates generally to systems and/or apparatus for improving the efficiency and/or operation of turbine engines, which, as used herein and unless specifically stated otherwise, is meant to include all types of turbine or rotary engines, including gas turbine engines, aircraft engines, steam turbine engines, and others. More specifically, but not by way of limitation, the present application relates to systems and apparatus pertaining to improved seals for turbine engines.
In general, a gas turbine engine (which, as discussed below, may be used to illustrate an exemplary application of the current invention) includes a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of blades that are axially or circumferentially stacked in stages. Each stage includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central axis or shaft. In operation, generally, the compressor rotor blades rotate about the shaft, and, acting in concert with the stator blades, compress a flow of air. The supply of compressed air then is used in the combustor to combust a supply of fuel. Then, the resulting flow of hot expanding gases from the combustion, i.e., the working fluid, is expanded through the turbine section of the engine. The flow of working fluid through the turbine induces the rotor blades to rotate. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated.
During operation, because of the extreme temperatures of the hot-gas path, great care is taken to prevent components from reaching temperatures that would damage or degrade their operation or performance. As one of ordinary skill in the art will appreciate, one area that is sensitive to extreme temperatures is the space that is radially inward of the hot-gas path. This area, which is often referred to as the inner wheelspace or wheelspace of the turbine, contains the several turbine wheels or rotors onto which the rotating rotor blades are attached. While the rotor blades are designed to withstand the extreme temperatures of the hot-gas path, the rotors are not and, thus, it is necessary that the working fluid of the hot-gas path be prevented from flowing into the wheelspace. However, axial gaps necessarily exist between the rotating blades and the surrounding stationary parts and it is through these gaps that working fluid gains access to the wheelspace. In addition, because of the way the engine warms up and differing thermal expansion coefficients, these gaps may widen and shrink depending on the way the engine is being operated. This variability in size makes it difficult to adequately seal these gaps.
Generally, this means that the turbine wheelspace must be purged to avoid hot gas ingestion. Purging requires that the pressure within the wheelspace be maintained at a level that is greater than the pressure of the working fluid. Typically, this is achieved by bleeding air from the compressor and routing it directly into the wheelspace. When this is done an out-flow of purge air is created (i.e., a flow of purge air from the wheelspace to the hot-gas path), and this out-flow through the gaps prevents the in-flow of working fluid. Thereby, the components within the wheelspace are protected from the extreme temperatures of the working fluid.
However, purging systems increase the manufacturing and maintenance cost of the engine, and are often inaccurate in terms of maintaining a desired level of pressure in the wheelspace cavity. In addition, purging the wheelspace comes at a price. As one of ordinary skill in the art will appreciate, purge flows adversely affect the performance and efficiency of the turbine engine. That is, increased levels of purge air reduce the output and efficiency of the engine. Hence, the usage of purge air should be minimized. As a result, there is a need for improved methods, systems and/or apparatus that better seal the gaps/wheelspace cavity from the working fluid, thereby reducing wheelspace ingestion and/or the usage of purge air.